1. Field of the Invention
The present invention relates to a method for implementing a system information broadcasting function in an asynchronous mobile communication system.
2. Background of the Related Art
The IMT-2000, a next generation mobile communication system, is required to assure global use in system design as well as system compatibility with a stationary network, and a high quality service. The IMT-2000 system is also required to assure a global roaming service, and to have an open system for easy introduction of future technologies and different applications thereto. Moreover, the IMT-2000 system is required to have a modular system to be ready for development to a more complicated system to cope with future service increases.
In general, a system information broadcasting in the asynchronous IMT-2000 system is implemented as follows.
When a RNC (Radio Network Controller) transmits system information to a base station through a system information update message in NBAP (Node B Application Protocol), the base station transmits the RSIM (RRC System Information Message) generated by system information contained in the system information update message to the air repeatedly according to a scheduling parameter defined in a RRC (Radio Resource Control layer). The system information in the asynchronous IMT-2000 system has one master information block, 2 scheduling blocks, and 19 system information blocks. The information blocks represent different system information, and a user equipment reads one of the system information block depending on its own status, a waiting range, and kind of a transmission channel which belongs to a base station the system information is transmitted therefrom. The RNC segments the master information block and the system information blocks to the first segment(short), a subsequent segment, the last segment(short), and a complete IB, and transmits to the base station through the system information update message. When the base station receives system information update message, the base station generates RSIMs using system information segment and scheduling parameter. Most of all, one RSIM is generated for one system information segment, but in some case, one RSIM consists of several system information segments. When the RSIM is smaller than 256 bits, a padding bit is added to the segment. A data unit obtained from the segmentation of the master information block (MIB) and the system information blocks (SIBs) is called an information block segment (IB segment). The base station transmits one RSIM to air at 20 ms intervals through a primary common control physical channel. FIG. 1 illustrates a diagram showing a relation between the system information block and the IB segment.
Each RSIM has 256 bits. In FIG. 1, because each of RSIM generated by the master information block, a first system information block, a second system information block, a third system information block, a fourth system information block, a seventh system information block, an eleventh system information block, and a twelfth system information block has a size not exceeding a size of one BCH (Broadcasting Channel) transmission block, each of them has only one segment. On the other hand, each of RSIM generated by a fifth system information block, and a sixth system information block in FIG. 1 has a size exceeding 3 BCH transmission blocks, each of the blocks is segmented into four segments.
As parameters for fixing a scheduling time of the system information, IB_REP, and SEG_POS are included. The IB_REP is a parameter representing intervals the system information blocks are transmitted to the air, and SEG_POS is a parameter representing a location of each system information block segment within a transmission period. As a value of the IB_REP for the master information block, 8 is assigned in a frequency division duplex mode, and, as a value of the SEG_POS for the master information block, 0 is assigned in the frequency division duplex mode. Other than the master information block, the IB_REP values for the system information blocks are given differently for different system information blocks, and the SEG_POS values are given differently for different information block segments. In other words, though system information block segments in the same system information block have the same IB_REP values, the system information block segments in the same system information block have different SEG_POS values. Table 1 shows one example of the IB_REP values and the SEG_POS values. Referring to FIG. 1, it can be known that segments in the same system information block have the same IB_REP values. FIG. 1A shows MIB includes IB_REP and SEG_POS. For ease of illustration, these parameters are not shown in the SIBs.
TABLE 1IBSegmentIB_REPSEG_POSIBSegmentIB_REPSEG_POSMIBSEG1 80SIB6SEG16414SIB1SEG1322SIB6SEG26422SIB2SEG1644SIB6SEG36426SIB3SEG1325SIB6SEG46430SIB4SEG16410SIB7SEG16434SIB5SEG16412 SIB11SEG16436SIB5SEG26418 SIB12SEG16442SIB5SEG36420SIB5SEG46428
The base station determines whether RSIM is transmitted to the air or not presently with reference to the IB_REP value and the SEG_POS value of the RSIM.
The base station (Node B) has an SFN counter for each cell. The SFN counter increases by 1 for every 10 ms in a count range of 0–4095 timer count. The SFN counter counts the SFN as ‘0’ when 10 ms is passed after a time point the SFN is 4095. The following equation (1) expresses a relation of SFNtx, a time point each of the RSIMs is transmitted to the air, and the IB_REP and SEG_POS, the parameters of the RSIMs.SFNtx % SIB_REP=SEG_POS  (1),That is, the base station implements scheduling of the system information block segments by a method in which the base station transmits the system information block segments to the air according to the equation (1). If there are several system information segments where are transmitted at same time, they consist of a RSIM.
The scheduling is a mechanism in which the system information block segments are transmitted to the air at different intervals by preset parameters. The equation (1) may be expressed as the following equation (2).SFNtx=IB—REP*n+SEG—POS, (0≦n≦M)  (2)
Where, the unexplained symbol ‘M’ represents a greatest value satisfying IB_REP*n<4096.
In summary, upon reception of the system information update message from the RNC, the base station is required to transmit respective RSIM generated by system information block segments at time points of the SFNtx values calculated by using the parameters of the IB_REP value and the SEG_POS value to the air, periodically.
By summarizing the foregoing steps, a process for implementing a system information broadcasting by the base station will be explained.
At first, upon reception of a system information update message from the RNC, the base station makes RSIM using information block segments and scheduling parameters, the base station stores all RSIMs of the master information block, scheduling block and the system information blocks, and the scheduling parameters of IB_REP and SEG_POS in a memory of the base station. Then, the base station searches the memory for a RSIM having scheduling parameters meeting the equation (1) for the SFN of the time point at every 20 ms, and transmits the RSIM to the air. The system information is information required to be transmitted always as far as the base station is in operation. Therefore, at the worst case, it is required to calculate the SFNtx for all the information block segments during the foregoing process by using the scheduling parameters at every 20 ms based on the equation (1), to require too much processing time for picking up a pertinent information block segment.